As is known, many liquid or pourable food products, such as fruit juice, UHT (ultra-high-temperature treated) milk, wine, tomato sauce, etc., are sold in packages made of sterilized packaging material.
A typical example is the parallelepiped-shaped package for liquid or pourable food products known as Tetra Brik Aseptic (registered trademark), which is made by sealing and folding laminated strip packaging material. The packaging material has a multilayer structure comprising a base layer, e.g. of paper, covered on both sides with layers of heat-seal plastic material, e.g. polyethylene. In the case of aseptic packages for long-storage products, such as UHT milk, the packaging material also comprises a layer of oxygen-barrier material, e.g. an aluminum foil, which is superimposed on a layer of heat-seal plastic material, and is in turn covered with another layer of heat-seal plastic material forming the inner face of the package eventually contacting the food product.
Packages of this sort are normally produced on fully automatic packaging apparatus, which advance a web of packaging material through a sterilization unit of the packaging apparatus for sterilizing the web of packaging material, e.g. by means of chemical sterilization (e.g. by applying a chemical sterilizing agent, such as a hydrogen peroxide solution) or physical sterilization (e.g. by means of an electron beam). Then, the sterilized web of packaging material is maintained and advanced within an isolation chamber (a closed and sterile environment), and is folded and sealed longitudinally to form a tube having a longitudinal seam portion, which is further fed along a vertical advancing direction.
In order to complete the forming operations, the tube is continuously filled with a sterilized or sterile-processed pourable food product, and is transversally sealed and subsequently cut along equally spaced transversal cross sections within a package forming unit of the packaging apparatus during advancement along the vertical advancing direction.
Pillow packages are so obtained within the packaging apparatus, each pillow package having a longitudinal sealing band, a top transversal sealing band and a bottom transversal sealing band.
In more detail, the package forming unit comprises a plurality of forming and sealing assemblies, each one, in use, forming and transversally sealing the tube so as to obtain the single packages. In particular, each forming and sealing assembly also transversally cuts the tube between two successive packages after or during the transversal sealing.
Each forming and sealing assembly comprises a sealing jaw for transversally sealing the tube for obtaining a respective transversal seal portion by locally compressing the tube and heating the heat-seal packaging material.
Different types of sealing jaws are known, which operate by means of induction or by ultrasound, in particular for heating the layers of heat-seal plastic material.
Sealing jaws which heat by means of ultrasound comprise an ultrasonic horn and an anvil, which, in use, compress the tube in cooperation with one another and by activation of the ultrasonic horn the heat-seal plastic material is heated and consequently melted so as to form the sealed transversal seal portion.
A typical anvil comprises a first ridge and a second ridge extending along respectively a first axis and a second axis and being arranged upon one another.
The anvil also comprises an elongated through-seat arranged between the first ridge and the second ridge for housing a cutting blade, which is adapted to transversally cut the tube along the transversal seal portion so as to define transversal sealing bands of the final packages. In other words, the cutting blade cuts, in use, the seal portion between a first sealing band and a second sealing band, which are substantially defined by respectively a first interaction surface and a second interaction surface of the anvil. The first sealing band being upstream of the second sealing band along the advancement path of the tube.
The first ridge and the second ridge respectively comprise the first interaction surface and the second interaction surface for contacting the tube.
Furthermore, the first interaction surface and the second interaction surface comprise respectively a first groove and a second groove each one adapted to receive a respective section of the longitudinal seam portion of the tube.
The first ridge and the second ridge also each comprises respectively the first interaction seam portion and the second interaction seam portion provided within respectively the first groove and the second groove each one, in use, interacting with a respective section of the longitudinal seam portion.
In particular, the first interaction seam portion and the second interaction seam portion are formed by three hemispheres for exerting in conjunction with the ultrasonic horn a local sealing pressure onto the respective section of the seam portion.
Even though the sealing jaws currently in use provide an efficient transversal sealing, a need is felt for further improvement.